The present invention relates to systems for intraluminally delivering and deploying self-expanding stents and other prostheses, and more particularly to such systems that incorporate mechanisms for retrieving partially deployed prostheses.
Stents, stent-grafts, and other body implantable tubular devices are employed in a wide variety of applications to maintain the patency of body lumens and guide the flow of blood and other body fluids through the lumens. These devices are employed in vascular applications, e.g. in pulmonary and thoracic vessels, and in arteries such as the coronary, renal, carotid, and iliac arteries. In addition to these vascular applications, the devices are used in the esophagus, duodenum, biliary duct, and colon. These devices may be either radially self-expanding or balloon-expandable in character. When deployed within body lumens, self-expanding devices radially expand into contact with surrounding tissue, typically assuming a diameter less than a fully expanded or relaxed state diameter. Consequently, an internal elastic restoring force acts outwardly against the tissue to assist in fixation of the device. Self-expanding devices frequently are preferred, due to this self-fixation capability.
Most applications employing radially self-expanding devices require intraluminal delivery of the device in a configuration suitable for delivery, i.e. radially compressed to a reduced-radius state against its internal elastic restoring force. To this end, prosthesis delivery systems frequently include two catheters: an outer catheter releasably containing the radially compressed prosthesis in a lumen near its distal end, and an inner catheter contained in the lumen, positioned against or otherwise engaged with the prosthesis. The prosthesis is deployed by moving the outer catheter proximally while holding the inner catheter in place. This effectively moves the inner catheter and the prosthesis distally relative to the outer catheter, allowing the prosthesis to radially self-expand as it emerges from the distal end of the outer catheter.
In either event, there arises on occasion a need to reverse the deployment. The need may arise from the physician's desire to reposition the prosthesis along the intended treatment site. Once a substantial portion of the prosthesis is free of the outer catheter, it may be moved in the proximal direction. However, at this point it is virtually impossible to move the prosthesis in the distal direction without retracting it proximally, back into the outer catheter. Accurate positioning of the prosthesis during deployment is challenging, in that it usually requires fluoroscopic imaging, and the difficulty is increased by the tendency of the many self-expanding devices to axially shorten as they radially self-expand. The need to retract a prosthesis can arise from other factors, e.g. a realization during deployment that a prosthesis of a different axial length or radius would be more effective at the designated treatment site.
In many conventional deployment and delivery systems, retraction of a partially deployed prosthesis is virtually impossible. To provide a retractable prosthesis, an inner catheter or other member can be surrounded by a high friction sleeve or gripping member as shown in U.S. Pat. No. 5,026,377 (Burton et al.), with the portion of an inner catheter supporting the sleeve and surrounded by the prosthesis. When the outer catheter radially compresses the prosthesis, it simultaneously presses the prosthesis into a frictional engagement with the sleeve. Accordingly, when the outer catheter is moved relative to the inner catheter, the prosthesis tends to remain with the inner catheter rather than following the outer catheter. A similar approach is shown in U.S. Pat. No. 5,817,102 (Johnson et al.) in which an exterior catheter radially compresses a stent into contact with a restraining sleeve that surrounds an interior catheter.
While these arrangements permit proximal retraction of a partially deployed stent or other prosthesis, they rely on a frictional engagement of the prosthesis with the inner member, through the gripping member or restraining sleeve. The force due to the frictional engagement must be sufficient to overcome the tendency of the prosthesis to move with the outer catheter as the outer catheter moves relative to the inner member. This frictional force acts in the axial direction, but requires a force acting in the radial direction to urge the prosthesis against the gripping member. The required radial force adds to the radial force already exerted by the prosthesis against the outer catheter due to its internal elastic restoring force, thus to increase the axial pushing force required to overcome friction between the prosthesis and outer catheter, and deploy the prosthesis.
Another factor inherent in this approach is the reduction in the frictional holding force as prosthesis deployment progresses, largely due to the diminishing portion of the prosthesis length subject to the frictional hold. As deployment progresses, the prosthesis becomes increasingly easy to deploy. Conversely, when the prosthesis is being pulled back into the catheter to reconstrain it, the reconstrainment force increases as more and more of the prosthesis is pulled into the catheter. This tendency can be counteracted by increasing the frictional holding force, but this in turn increases the radial force required to overcome the frictional hold, once again increasing the force required for ordinary deployment.
Other arrangements involve axially tight or locking engagements of prostheses with inner member coupling structures. Examples of these arrangements are seen in U.S. Pat. No. 6,350,278 (Lenker et al.) and U.S. Pat. No. 5,733,325 (Robinson et al.). These systems permit prosthesis retraction, but impose unduly stringent tolerances upon the coupling structure. Further, they require close attention and care on the part of the physician or other user when loading a prosthesis into the system, to ensure that the required coupling is achieved.
Therefore, the present invention is disclosed in terms of several embodiments, each directed to at least one of the following objects:                to provide a prosthesis deployment system with the capability of retracting partially deployed prostheses, without any substantial increase in the axial forces required to deploy the prostheses;        to provide a prosthesis deployment system that permits retracting of the prosthesis at a later stage in its deployment, in terms of the fraction of the prosthesis axial length exposed, without degrading or losing retraction capability;        to provide a deployment device that has greater stent retention capability if the need arises for withdrawing a partially deployed stent;        to provide a deployment device capable of retracting partially deployed device in which an open-frame support structure is covered, e.g. as in stent-grafts; and        to provide a prosthesis anchoring device suitable for attachment to an inner catheter or other inner member of a conventional prosthesis delivery and deployment system to provide the capability of retracting partially deployed prostheses.        